1. Field of the Invention
The present invention relates to a magnet brush type developing device in an electrophotographic copying machine and the like.
2. Description of the Prior Art
As is generally known, a magnetic brush type developing means is equipped with a developing sleeve that is rotatably stored in a box-like housing containing developer and which includes a plurality of permanent magnets, an agitating blade rotatably mounted in the bottom of the housing positioned behind said developing sleeve and which frictionally electrifies toner by agitating, and a doctor blade provided inside the housing facing the circumferential surface of said developing sleeve for regulating the thickness of a developer layer formed on the circumferential surface of the developing sleeve by the magnetic flux of the permanent magnets.
Heretofore, in an electrophotographic copying machine using the magnetic brush type developing device, there was a tendency to increase the driving speed of each part of the machine in order to increase the hourly processing capability. In the high speed copying machine of this kind, the consumption of toner is remarkably increased. The increase in toner consumption necessitates the increase of rotation speed of the developing sleeve and the agitating blade in the magnetic brush type developing means. Consequently, in the housing of said magnetic brush type developing device, a large quantity of floating toner is produced owing to high speed rotation of the agitating blade. The floating toner rides on the air current in the chamber which has been accompanied by the rotating motion of the developing sleeve, is discharged from the housing, and then is adhered to various processing devices in the copying machine, thus to cause a variety of difficulties.
To cope therewith, the present inventors have attempted the countermeasure in providing a vacuum inlet port at the opening of the developing device to remove floating toner being discharged from the housing, and the countermeasure in narrowing the gap between the internal surface of the housing and the circumferential surface of the developing sleeve, which is the path of the floating toner being discharged. However, those countermeasures were confronted with the following problems. That is, in the countermeasure in providing a vacuum inlet port, it is possible to remove the floating toner. However, with a high speed developing device, floating toner is discharged in large quantity and a filter is stopped or clogs too early. Therefore it was difficult to put this first countermeasure to practical use. In the construction in narrowing the discharging path, it was expected that the discharge of floating toner could be obstructed by the ears of developer formed on the circumferential surface of the developing sleeve. However, the construction was not very effective and the discharging quantity of floating toner was not changed very much compared with that before the countermeasure was taken.